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VMWARE ESXI configureation

Posted on 2014-07-15
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I inherited few vmware servers.  They're 4  quad xeon servers with hyperthreading and 64 gb of RAM.  The ESXI is an enterprised version.   Some of the VM's are configured with 8 virtual processors and 8-24 gb of ram.  About 8 VMs are running on each host.  Are there advantages of using over 2 virtual processors?   Is it necessary to allocate 24 gb of Ram to virtual machine.
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Question by:jem1662
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ID: 40197089
Your VMs seem to hive too many vCPUs allocated.

Very often you do not need more than 2 vCPUs
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by:jem1662
ID: 40197129
Are the best practice for virtual processors and guest memory usage?
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by:markvor
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What Software is installed inside the VM's ?
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by:jem1662
ID: 40197722
Windows 2008 R2 Server,  some vms have small sql server database,  some have oracle and one vm has a product called QLIKVIEW.
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 40197995
vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectly, e.g. Servers than can use vSMP correctly :- SQL Server, Exchange Server.

This is true, many VMware Administrators, think adding lots of processors, will increase performance - wrong! (and because they can, they just go silly!). Sometimes there is confusion between cores and processors. But what we are adding is additional processors in the virtual machine.

So 4 vCPU, to the VM is a 4 Way SMP (Quad Processor Server), if you have Enterprise Plus license you can add 8, (and only if you have the correct OS License will the OS recognise them all).

If applications, can take advantage e.g. Exchange, SQL, adding additional processors, can/may increase performance.

So usual rule of thumb is try 1 vCPU, then try 2 vCPU, knock back to 1 vCPU if performance is affected. and only use vSMP if the VM can take advantage.

Example, VM with 4 vCPUs allocated!

My simple laymans explaination of the "scheduler!"

As you have assigned 4 vCPUs, to this VM, the VMware scheulder, has to wait until 4 cores are free and available, to do this, it has to pause the first cores, until the 4th is available, during this timeframe, the paused cores are not available for processes, this is my simplistic view, but bottom line is adding more vCPUs to a VM, may not give you the performance benefits you think, unless the VM, it's applications are optimised for additional vCPUs.

See here
http://www.vmware.com/resources/techresources/10131

see here
http://www.gabesvirtualworld.com/how-too-many-vcpus-can-negatively-affect-your-performance/

http://www.zdnet.com/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios-4010025185/

also there is a document here about the CPU scheduler

www.vmware.com/files/pdf/perf-vsphere-cpu_scheduler.pdf

https://blogs.vmware.com/vsphere/2013/10/does-corespersocket-affect-performance.html

As for RAM allocation in the VM, is it necessary, how much is in use....you could reduce it, at no performance decrease, but check your performance.
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by:jem1662
ID: 40198388
Thank You for the info.
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